It could be because conditions change too rapidly. Whatever you are buying and selling this week, it might be different next week. I know someone who sells a l

It could be because conditions change too rapidly. Whatever you are buying and selling this week, it might be different next week. I know someone who sells a lot of stuff on amazon. It's mostly books, but they do a little retail arbitrage type stuff too. Sometimes it can be as simple as a store in their area having bought too much of something, so they put it on sale, whereas a store in someone else's area didn't, so there's the price difference. Or it can be a discontinued product that is still in demand but stores in one city have extra whereas stores in another city are out. The whole point of arbitrage is that you identify and exploit price imbalances. But imbalances tend to balance themselves out eventually, so it's often a temporary situation.